This invention relates to the interrogation of samples by monochromatic light and, in particular, relates to a diffraction grating produced monochromatic light and an apparatus and process for screening out half order wavelength effects from diffraction gratings.
1. Statement of the Problem
It is common to observe during centrifugation separation of sample. Typically, a centrifuge rotor is provided. The rotor includes a so-called sample cell and a reference cell. To enable the observation, the sample cell and the reference cell are supplied with windows. Light is transmitted through both sample cell and the reference cell.
The reference cell and the sample cell preferably both contain a solvent having a gradient forming solute therein. During the centrifugation process, the absorption of the light radially across the reference cell provides an indication of solvent and solute gradient in both the reference cell and the sample cell. The relative absorption of light radially across both sample cell and the reference cell provide an indication of sample separation. By observation of both the solute gradient in the solvent and sample separation, analysis may be made and distribution in the gradient forming solute within the solvent.
For such light of the sample/absorption measurement, monochromatic light has been used. Typically, measurements are taken in a variety of discrete wavelengths. By observation of light absorption of a sample cell versus a reference cell at the same discrete wavelength, identification, quatification, and related analysis of the components of the sample can be made.
It has been known to utilize narrow band pass filters to produce the desired monochromatic light. Unfortunately, these filters are large, have many optical interfaces and are expensive. Further, where several wavelengths are utilized, the mechanical problem of sorting, inserting and removing the filters to and from the interrogating light path complicates filter usage.
2. Related Art
In a related disclosure entitled UV Scanning System for Centrifuge. Ser. No. 07/115.023, filed Oct. 29. 1987, now U.S. Pat. No. 4,830,493, I have disclosed the use of a diffraction grating for producing monochromatic light for sample absorption analysis. Simply stated. I disclose a mirror diffraction rule parallel to a tilting axis to produce monochromatic light. The mirror has a figure along the length of the axis with appropriate curvature to produce collimated interrogating light. By the expedient of tilting the mirror, interrogation of windowed cells in a rotating rotor can occur by monochromatic collimated light beams during the process of centrifugation.